The present disclosure relates to a multi-effect desalination apparatus partially dosing acids into evaporators of a high temperature and to a desalination method using the same, and more preferably relates to a technique for increasing the top brine temperature (TBT) of a multi-effect desalination apparatus by additionally dosing acids partially, that is, only into the evaporators corresponding to a high temperature part (H), to minimize a risk of scale and corrosion together with an anti-scalant.
Generally, a desalination facility is one producing fresh water which can be used as water for living or industrial use from seawater or wastewater, and Multiple Stage Flash (MSF) and Multi-effect Distillation (MED) methods are mostly used, as well as Reverse Osmosis (RO) which uses pressure as a membrane filtration. A hybrid type combining two or more of these methods is also used to increase an output of fresh water and effectiveness.
Among these, a desalination facility by the multi-effect distillation is equipped with an evaporator comprising several effects and with multiple heat exchange tubes wherein high-temperature steam is passed through an interior heat exchange space of each effect and feed water is sprayed onto the exterior.
In addition, each evaporator is constructed so that the steam is fed by connecting each effect by a steam feed tube from the first effect, the produced water generated from each evaporator is connected to a recovery line of fresh water to be discharged by a fresh water pump, and a concentrated water with high concentration is discharged to the exterior through a discharge.
First, high-temperature steam is fed to the evaporator (100A) of the first effect and feed water is sprayed through the spray nozzle while making the heat exchange on the surface of the heat exchange tube. Therefore, the steam in the interior of the heat exchange tube is condensed to make fresh water, simultaneously with generating the steam in the heat exchange space in the interior of the evaporator, and the generated steam acts as a heat source to the evaporator (100B) of the next effect through the steam feed tube. The continuous heat exchange can be completed in evaporator (100N) of the most downstream evaporator.
Various efforts have been made to prevent the scale formed by hardness materials included in the feed water in the common desalination facility such as MED, MSF, and the like. There was a method for inhibiting a formation of scale by acid treatment, but since it should accompany an installation of an additional decarbonizing/degassing facility together with the risk for corrosion, the method was avoided due to problems such as additional electrical power consumption, and its use disappeared with the development of a polymer-based anti-scalant.
However, the scale risk for an evaporator corresponding to a ‘high temperature part’ of a number of evaporators, especially the upstream part was not sufficiently resolved only by the newly developed anti-scalant, and thus, since the desalination facility cannot be driven with the top brine temperature (TBT) set higher than a certain level, there were problems of reduced economical efficiency or effectiveness.
Therefore, Laid-open Korean Patent Publication No. 2010-0016519 (‘Desalination apparatus and method’, published on Feb. 12, 2012) disclosed a method for increasing the top brine temperature of the desalination facility by separately installing a Nano Filter (NF), RO membrane, etc. on the front of the desalination facility to remove beforehand the material generating the scale, but the method is inefficient since it needs a large-scale facility for the additional pre-treatment and thus increases the CAPEX and OPEX of all processes.